1. Field of the Invention
The present invention relates generally to a suspension control system for an automotive vehicle. More specifically, the invention relates to a technology for suppressing vehicular rolling motion with enhanced responsive characteristics.
2. Description of the Background Art
Various suspension control systems have been proposed in order to achieve both vehicular riding comfort and driving stability. In such suspension control systems, suppression of vehicular rolling is one of the most important factors in measuring control performance. For example, Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 62-72811 discloses a roll suppressive suspension control system. The above-identified prior proposed system employs a variation in a rate of lateral acceleration for detecting a vehicular rolling condition in a magnitude requiring a harder suspension.
As will be appreciated, in such rolling suppressive suspension control utilizing lateral acceleration exerted on the vehicular body, a vehicular rolling condition for hardening suspension characteristics can be detected only after a certain magnitude of vehicular rolling motion is actually caused. In view of this, it is preferred to detect the vehicular rolling state at a timing as early as possible. In this aspect, a variation in a rate of lateral acceleration may be advantageously introduced rather than a magnitude of its lateral acceleration because of higher response characteristics. Namely, at the beginning of vehicular rolling, a gradient of a variation of the variation rate of lateral acceleration is greater than that of lateral acceleration to make it easy to detect vehicular rolling. However, on the other hand, when the vehicle travels through a relatively long and constant radius curve, the variation rate becomes zero at the intermediate portion of the curved road due to a constant angular position of the vehicular steering. In such case, when the variation rate of the lateral acceleration is employed as the vehicular rolling condition detecting parameter, discrimination between the vehicular condition steadily traveling on a straight road and a curved road can not be made despite actual rolling caused on the vehicle. This results in a softening of the suspension characteristics despite exertion of the lateral acceleration in a significant magnitude to increase rolling magnitude.